[Product Innovation]
Router-On-A-Chip Manages Network Traffic With Wire-Speed QoS
Full-custom design techniques are the key to building an IC with 16-Gbit Ethernet ports and an impressive list of networking features.
Stuffing 16-Gbit Ethernet ports into a single IC is no mean feat. But doing this created the CXE-16, a so-called router or switch on a chip. Even more impressive, the IC is fabricated in 0.25-µm CMOS technology. According to SwitchCore, the Swedish-based company that developed the IC, the CXE-16 replaces upwards of 25 chips used in some router or switch designs.
The company has integrated onto a single chip all of the media-access controllers (MACs), switch engines, and memory needed for a 16-port Gigabit Ethernet router. Data coming into the receive MACs travels through a path that includes a serial-to-parallel converter, shared-buffer memory, and a parallel-to-serial converter. It exits through transmit MACs (Fig. 1).
The CXE-16 can handle 16-ports of full-line-rate gigabit traffic. All packets are queued on the transmit side to avoid head-of-line (HOL) blocking. To deal with overflows in the shared-buffer memory, the chip employs a RAMBUS interface for external RAMBUS memory.
It also contains 8k addresses of content-addressable memory (CAM). This amount is typical for the workgroup or small enterprise. Larger applications, of course, may require more CAM entries. Up to seven external CAMs can be added to these applications for a total of 232,000 addresses (Fig. 2).
To achieve the high integration level of the CXE-16, the company uses full-custom design, placing transistors on the chip in a very logical and orderly fashion. This methodology has several benefits, including full utilization of performance potential, power savings, and process opportunities.
Unlike a semi-custom design, the full-custom procedure optimizes the chip's routing or layout. This method distributes the clock signal, too. Clock paths can be placed right next to datapaths and, for the most part, clock and data remain synchronized.
Generally, full-custom chips are more compact. SwitchCore believes designers may use 0.25-µm full-custom technology in situations where they currently employ a 0.18-µm semi-custom technology. But overall performance will be better.
Beyond its 16 ports of 10-/100-/1000-Mbit Ethernet, the CXE-16 hosts many features. It has the ability to filter and classify data for layers 2, 3, and 4 of the International Standards Organization's Open Systems Interconnect (OSI) reference model. Consequently, it guarantees both bandwidth and quality of service (QoS) based on programmable options.
Users will find that the device is very flexible. With eight queues in each output port, QoS can be split into eight groups per output. The 512-kbyte on-chip CAM can be extended by using another SwitchCore chip, the CXE-5000.
If an external buffer is used, it would have RAMBUS memory. In the process, data transfers at 1.6 Gbytes/s. A lot of data goes through this switch, which is why RAMBUS is used for fast buffering.
The chip also has automatic MAC address learning. It immediately learns the L2 address of any new device plugged into it. The CXE-16 boasts full 4-kbyte VLAN support as well.
On the chip, the interface is "glueless" to a Motorola PowerPC. Because it's a 32-bit interface, it can be used with other CPUs. However, it may need some glue logic.
The device offers port mirroring for testing and debugging, along with link aggregation for extra bandwidth on a certain link. Such aggregation is called port trunking. Spanning-tree and flow-control support also are in the CXE-16, as are statistics counters for SNMP, RMON, and SMON protocols. The physical-layer (PHY) interfaces are designed to connect gluelessly at 1-Gbit/s to a fiber PHY. The GMII and MII interfaces gluelessly attach to a copper PHY.
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